In a printing system a stack of paper or other print media is typically loaded at a media input location, from which the media is moved, one sheet at a time into a printing region for printing, and then is discharged from the printer. In order to pick one sheet at a time from the media input location, generally a paper separator is located between the media input location and the printing region. If the paper is loaded too far into the printing mechanism, such that the lead edge of more than one sheet of paper is past the paper separator, multiple sheets can inadvertently be fed, leading to paper jams and possible damage in the printer. It is well-known to incorporate a media stopper to keep the lead edges of the stack of paper from advancing beyond the paper separator, until it is desired to move a sheet into the printing region for printing, and then retract the media stopper to let the sheet pass. Printing systems include line printing systems, which print a line of pixels substantially at one time (using a page-width printhead for example), and a carriage printer, which prints a swath of pixels. The examples described here will be for a carriage printer, but there can also be applicability for a line printing system.
In a carriage printer, such as an inkjet carriage printer, a printhead is mounted in a carriage that is moved back and forth across the region of printing. To print an image on a sheet of paper or other print medium, the medium is advanced a given nominal distance along a media advance direction and then stopped. While the medium is stopped and supported on a platen, the printhead carriage is moved in a direction that is substantially perpendicular to the media advance direction as marks are controllably made by marking elements on the medium—for example by ejecting drops from an inkjet printhead. After the carriage has printed a swath of the image while traversing the print medium, the medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath.
FIG. 1 shows a schematic side view of a prior art carriage printer having a so-called L-shaped paper path. A variety of rollers are used to advance the medium through the printer. In this example, a pick roller 350 moves the first piece or sheet 371 of a stack 370 of paper (also generically called recording medium herein) at media input support 320 from paper load entry direction 301 toward media retention plate 340. Media retention plate 340 is disposed along media advance direction 304 and is at an angle α with respect to media input support 320. Angle α is typically greater than 60 degrees, so that when seen from the side view of FIG. 1, media input support 320 and media retention plate 340 look approximately like a letter L. A media stopper element 342 is indicated in FIG. 1 as a dotted line extending upward at an angle from media retention plate 340. The dotted line position is the normal position of the media stopper element, in order to prevent media from advancing past the media separator (not shown). When paper is being moved out of the media input support for printing (as in FIG. 1), the media stopper element 342 is retracted into the media retention plate 340. After the piece 371 of recording medium moves past the retracted media stopper element 342 and the media separator, it is then moved by feed roller 312 and idler roller(s) 323 to advance through the print region 303, and from there to a discharge roller 324 and star wheel(s) 325. Carriage 200 moves a printhead die 251 along a carriage scan direction that is into the plane of FIG. 1 and ink drops 270 are controllably ejected to print an image as the carriage is moved. Supporting the piece 371 of recording medium at print region 303 is a platen 390. In order to facilitate the printing of borderless prints where the image is printed to the edges of the recording medium, platen 390 can have support ribs 394 in between which is disposed an absorbent medium 392 to catch ink drops that are oversprayed beyond the edges of the recording medium.
Competitive cost pressures, particularly for printers that are used in the home, drive efforts to reduce components such as motors in a printer. For example, in a carriage printer it is a goal to have one motor that moves the carriage, and another motor that provides power for moving the paper, as well as other motions in the printer. What is needed is a simple, low cost and reliable way of moving the media stopper elements into a retracted position during picking of media from the media input support, and otherwise having the media stopper elements extending from the media retention plate to prevent the lead edges from moving too far into the printing mechanism.